Printed wiring boards (PWBs) are used extensively to produce electronic circuits. PWBs are typically formed as sandwiches of one or more layers of dielectric material and one or more layers of conductive material, in which the conductive material may be formed, by etching, into patterns including lines, known as traces, which form connections in a circuit. Holes with conductive walls, known as vias, may be formed in the dielectric layers to provide electrical connections between conductive layers.
A circuit on a PWB may include connectors, and components such as resistors, capacitors, or transistors, which may be installed on the PWB by applying solder paste to the outer conductive layer at the locations where the components are to be installed, placing the components on the PWB, and heating the assembly in a solder reflow oven which melts the solder, soldering the components in place. Alternately, conductive epoxy may be used instead of solder.
Coaxial connectors known as board edge-launch connectors may be installed at the edge of a PWB to provide connections to other parts of a system. For example, a PWB with an array of connectors along one edge may be installed in a system by sliding it into a chassis so that the connectors on the PWB connect simultaneously to an array of corresponding mating connectors in the chassis. Such an arrangement, in which there is no opportunity for a human operator or technician to align and connect the connectors individually and where the technician may not be able to see the connectors, is known as a blind-mate application.
Coaxial connectors individually soldered to a PWB may be unsuitable for use in a blind-mate application because the process for soldering such connectors to a PWB may not produce sufficiently precise alignment to allow each connector to connect reliably with the corresponding connector in an array, such as in the chassis-based system described above. In such a case it may be helpful to use a single rigid part known as a connector frame to hold all of the connectors, and to maintain their alignment relative to each other and to a PWB. It may also be convenient to have the connector frame secured to the bottom surface of the PWB, providing a ground connection between the connector frame and a ground conductor on the bottom surface of the PWB.
When a connector frame is used with coaxial connectors, it may be necessary to provide ground connections also between the outer conductors of the connectors and ground conductors on the top surface of the PWB. Moreover, when the connectors will be carrying high-frequency signals, such as radio frequency (RF) or microwave signals, it may be necessary to have a continuous connection from the connector frame to one or more ground conductors on the top surface of the PWB, forming a transmission line, so that the characteristic impedance of the signal path will be uniform and to prevent reflection or radiation of the signal.
A connection between the connector frame and the top-layer ground conductors may be formed by bonding wires to the connector frame and to top-layer ground conductors near the edge of the PWB. A bond wire, however, generally follows a curved path through air between the bond pads it connects. This causes the corresponding part of the signal path to have a different, and generally high, characteristic impedance, and if the wire bonds are applied under manual control, the wire path and the characteristic impedance may suffer from poor repeatability. Moreover, wire-bonding machines may be designed to work with relatively small parts, and a PWB with a connector frame may be too large to fit into such a machine.
Another means of forming a ground connection between the connector frame and a top-layer ground involves applying a globule of conductive epoxy manually to a ground conductor near the edge of the PWB and to a nearby surface of the connector frame, so that the epoxy bridges the gap between the connector frame and the top-surface ground conductor on the PWB. This method is unsatisfactory, primarily because of the conflicting requirements of (i) applying a sufficient quantity of epoxy to ensure that the gap is bridged by the epoxy and that contact is made reliably with both the connector frame and the PWB, and (ii) applying a sufficiently small quantity of epoxy that it will not flow to other nearby conductors, thereby forming unwanted short circuits. These difficulties may be compounded by variations in gap width resulting from fabrication tolerances, and from the poor repeatability of a manual process.
Thus, there is a need for a system for providing connections between a conductive connector frame and one or more conductive areas on the top surface of a PWB.